Various types of natural and synthetic diamond products are known and commercially available for industrial use. These diamond products are typically used in tools that require high strength cutting elements. For example, various diamond products are used as the cutting elements in earth boring drill bits, in dressing and cutting tools (e.g., saw blades), in machining and woodworking tools (e.g., lathes), and in wire drawing dies. Diamond products are also used in applications demanding high wear resistance, for example, as bearing surfaces. In recent years, techniques have been developed for manufacturing high quality polycrystalline diamond compacts (PCD's) and incorporating such compacts into the cutting elements of these tools. Such compacts have demonstrated advantages over single crystal diamond cutting elements, such as improved wear and impact resistance.
Initially, the polycrystalline diamond compacts commercially available were thermally stable only up to a temperature of about 750.degree. C. This limited their usefulness since the temperatures reached for certain uses exceeded 750.degree. C. Additionally, this temperature severely restricted many of the processing steps for bonding the polycrystalline diamond compacts to tool bodies. Later on, polycrystalline diamond materials became available which have a temperature stability up to about 1200.degree. C. An example of an unleached polycrystalline diamond compact having a temperature stability up to about 750.degree. C. is a product sold under the tradename STRATAPAX by the General Electric Company, while an example of a polycrystalline diamond compact having a temperature stability up to 1200.degree. C. is a product sold under the tradename GEOSET, also by the General Electric Company. Other polycrystalline diamond materials which are available in the marketplace are SYNDAX-3 and SYNDRIL, both available from De Beers.
These synthetic polycrystalline diamond compacts are characterized by sintered diamond to diamond bonds, are superhard, and have high diamond concentrations, typically in the range of about 80-95% by volume. Furthermore, they are manufactured under the ultra-high temperature and pressure conditions of the diamond forming region (above 40 kbars and between 1200.degree. C.-2000.degree. C.) in the presence of a catalyst/solvent which promotes diamond to diamond self-bonding. Consequently, these polycrystalline diamond products are of very high quality but are also costly to manufacture.
The high quality polycrystalline diamond products discussed above perform exceptionally well in drilling various rock formations. Drill bits incorporating the STRATAPAX compact, for example, have a wear resistance about 200 times that of drill bits with cemented tungsten carbide cutters when cutting Barre granite, and even greater when drilling other kinds of rock formations. However, there are many soft-rock formations which do not require such high quality products. For example, some shales, limestones and sandstones do not require a drill bit with the exceptional wear resistance of synthetic polycrystalline diamond compacts. In the past, such soft-rock formations have been drilled using non-diamond drill bits having, e.g., cemented tungsten carbide cutters or mill tooth bits made of steel.
While such soft rock formations do not require high quality synthetic polycrystalline diamond compact cutters, they do require cutters somewhat better than those employing cemented tungsten carbide inserts, steel mill tooth bits, or other non-diamond drill bits. This is because the soft rock formations are frequently intermixed with abrasive rock layers or stringers within their depths. Conventional non-diamond cutters are satisfactory for drilling through most of the soft rock formations. However, once an abrasive rock stringer is encountered, the cemented tungsten carbide cutters or steel mill tooth bits wear out very rapidly and may not cut any longer.
In addition to their use in the form of polycrystalline diamond compacts for cutters, diamond particles have also been used to impregnate abrasive cutting elements, such as abrasive grinding wheels and saw blades. Typically, the cutting elements are formed from a mixture of tungsten carbide powder, cobalt and diamond dust. See, e.g, U.S. Pat. Nos. 2,818,850 and 2,796,706. The diamond concentration in such impregnated products is generally less than 40% by volume.
Various techniques have been developed for improving the retention of diamond products to a backing. For example, it is known in the prior art to coat diamond particles with various metals, such as tungsten, tantalum, chromium, niobium, or molybdenum. The metallic coating may be applied to the surface of the diamond particles by a variety of known techniques, such as by sputtering, by chemical vapor or vacuum deposition, or by electrolytic or electroless coating. See, e.g., U.S. Pat. No. 3,879,901 (Caveny), and U.S. Pat. Nos. 3,841,852 and 3,871,840 (Wilder et al). An example of a method for depositing a metal coating (e.g., Cr, V, W, Mo, Ti, Mn, or Nb) onto the surface of diamond or cubic boron nitride (cBN) particles is disclosed in U.S. Pat. No. 4,339,17 (Pipkin). In application Ser. No. 261,236, commonly assigned with the present application, a technique is taught for improving the retention of diamond particles by applying multiple coating layers to the particles.
Once coated, the prior art teaches that the coated diamond particles or grits may be formed into various shapes by hot or cold pressing, and subsequent sintering or infiltration with brazing alloys. In general, these techniques have been used in connection with single crystal diamond particles, with high quality polycrystalline diamond compacts having a diamond concentration in excess of 80%, or with diamond impregnated products having a diamond concentration of less than 40% by volume.
In U.S. Pat. No. 4,378,975 (Tomlinson), for example, a tool insert is disclosed which comprises discrete chromium-coated diamond particles bonded together during a sintering process by means of a nickel-based alloy having a melting point below about 1100.degree. C. The concentration of diamond particles in the final product is in the range of about 10 to 40% by volume. The diamond particles generally have a size of 200 microns or larger.
From the above discussion, it will be seen that two kinds of synthetic diamond cutting elements are currently available. The first kind contains high quality polycrystalline diamond compacts. These compacts are more than 80% by volume diamond, are made under high pressure, high temperature ("HPHT") conditions, are characterized by sintered diamond to diamond bonds, and are expensive to manufacture. The other kind of synthetic diamond cutting element contains the less expensive impregnated product. This kind of cutting element is less than 40% by volume diamond and is of much lower quality than a polycrystalline diamond cutting element. There are no synthetic diamond cutting elements available which are cheap to manufacture and are of intermediate quality, namely, having a diamond concentration in the range of above about 40% to about 75% by volume. Such cutting elements would find use in all typical applications for synthetic diamond products, but would be especially useful in earth boring drill bits for drilling soft rock formations, such as shale formations.
Accordingly, there is a need to provide a synthetic diamond cutting element made from a diamond-metal composite having a concentration of diamond or another superhard material in the range of above about 40% to about 75% by volume.
There is a further need to provide a cutting element of the kind mentioned above wherein the diamond particles ar metallically and/or chemically bonded to each other and, optionally, to a backing member, by an infiltrating alloy which forms a cementing matrix for the coated diamond particles.
There is a further need to provide a cutting element of the kind mentioned above which is suitable for use in a earth boring drill bit for drilling soft rock formations with intermixed abrasive rock stringers.
There is yet another need to provide a relatively low cost method for manufacturing a cutter of the kind mentioned above, which method employs pressures and temperatures well below those of the diamond forming region.